Mercury column thermostatic switch



Mayvl3, 1952 w. M. SMITH ETAI. 2,596,825

MERCURY COLUMN THERMOSTATIC SWITCH Filed Feb. 17, 1949 Patented May 13, 1952 UNITED STATES PATENT OFFICE MERCURY COLUMN THERMOSTATIC SWITCH Application February 17, 1949, Serial No. 76,954

4 Claims.

This invention relates to thermostats of the mercury column type in which an electrical contact wire extends through the wall of a thermostat tube for engagement with the mercury column.

A principal object of the invention is to provide, in a thermostat of the above general class, a new and improved arrangement of the electrical contact wire so as to insure more reliable contact with the mercury column than is ordinarily obtained in thermostats made and used prior to this invention.

It has been customary, heretofore, to arrange the electrical contact wire in the glass wall of a thermostat tube so that the wire will extend radially outwardly from the inner wall of the central bore of the tube, but such position of the contact wire has been attended with various di'iculties, both in the construction of the thermostat and in the operation of the thermostat. Such operating difficulties are due largely to imperfections in the manufacture of the thermostat. For example, the glass tube is ordinarily severed, as contemplated in the present invention, to permit the wire to be inserted, the end of the wire being arranged flush with the inner wall of the central bore of the tube. However, it is extremely difficult to maintain the said end of such wire in its proper position relative to the inner wall of the tube. since it is held in position only at one end and by the pressure of the previously severed sections of the tube while the tube is being heated to a plastic state to rejoin the said sections. Under such condition the displacement of the glass around the contact wire, which wire is made of platinum and is of very small diameter, frequently presses the molten glass over the end of the wire so as to insulate its end from the mercury column of the thermostat or to materially reduce the contact area. In some instances the wire extends into the bore of the thermostat tube so as to objectonally reduce its cross sectional area and, by reason of burred end of the wire and its endwise position in the central bore of the tube, retard the movements of the mercury column. The burred end of the wire, due to the cutting of the wire, has a tendency to restrict the initial contact with the mercury column, since the molten glass sometimes flows over the wedge-shaped surface formed at the end of the wire by the shearing operation.

According to the present invention, the glass thermostat tube is cut at a desired location for the insertion of the contact wire and the wire, instead of extending only to the surface of the ZOU-141) central bore of the tube, extends entirely across the tube on a line which intersects the circumference of the central bore at one side thereof so that a smooth lateral surface of the wire protrudes slightly into the said central bore to an extent equal to approximately one-eighth of the diameter of the wire. In this position of the contact wire it slightly constricts the central bore of the tube, but its smooth lateral surface does not retard the movement of the mercury through the restricted portion of the bore. This arrangement of the wire relative to the central bore of the glass tube exposes a substantially larger surface of the wire for contact with the mercury column of the thermostat than is ordinarily obtainable when the contact wire is arranged with an end surface terminating at the Wall of the bore of the glass tube. The smooth lateral surface of the wire, being of larger area than the end area of such wire, assists in producing a phenomena during the manufacture of the thermostat, whereby the column of mercury, when heated to a selected temperature corresponding to a desired temperature setting of the thermostat, may be readily and accurately separated at the contact wire by flicking the upper end of the tube in a direction to remove the surplus mercury from the central bore. It has been found that in most instances the mercury column will accurately separate at such contact Wire. Apparently the wire provides a uniform scoring of the mercury column at the restricted area of the bore of the tube and also reduces the surface tension at the wire whereby the inertia, during the arcuate flicking movement of the tube separates the mercury column at the contact wire.

Another and more specific object of the invention is to provide, in a mercury column thermostat, an improved arrangement of the contact wire whereby both ends of the wire serve as electrical connectors whereby either end will function to complete a circuit from the mercury column in the event that the other end of the contact wire becomes sheared off near the outer surface of the tube.

One approved form of the invention is illustrated in the accompanying drawing wherein:

Fig. l is a view shown partly in elevation and partly in section of a thermostat constructed in accordance with this invention.

Fig. 2 is a view partly in section and partly in elevation illustrating a partly formed thermostat tube.

Fig. 3 is a fragmentary sectional view on a 3 greatly enlarged scale taken on line 3-3 of Fig. 2, and

Fig. 4 is a similarly enlarged longitudinal section of a portion of the tube adjacent a contact wire of the tube but omitting the contact ring shown in Fig. 1.

Referring first to Fig. 1 of the drawing wherein a completed thermostat is shown: The main body of the thermostat tube is designated by the reference numeral I9. It is formed at its lower` end with a bulb Il of predetermined size to provide a storage chamber for the mercury used in the thermostat. The main body I) is formed with a relatively small central bore I2 which extends from the mercury reservoir II to vthe upper end of the tube and terminates at its upper end in a small bulb I3. Y

The speciiic form of thermostat shown herein includes two contact wires designated I4 and I5. rljhe lower contact wirer I4 is positioned so that it will be in continuous contact with the mercury column I6. The upper contact I5 is positioned at a predetermined location whereby the mercury column, when expanded by a predetermined temperature, will make contact with the said contact I5. The contact wires I 4 and I5 have diameters considerably smaller than the diameter of the bore in the tube and extend entirely through the glass tube of the thermostat, but are arranged at one side of the longitudinal center so that its smooth lateral face will extend into the central bore I2 of the tube a distance approximating one-eighth of the diameter of the wire whereby the centralpoint I 1 of the wire will be exposed to the interior of the said bore I 2 and thereby provide an electrical connection between the contact wires and the mercury column of the thermostat.

The opposite ends of each wires I4 and I5 are suitably soldered or otherwise embedded in metallic lines Mfr-ISE, the latter of which provide means to which electrical lead wires hib-I5b may be attached.

In order to accurately position the wires I4 Y and I5 in the glass tube, the tube is severed at the location where the contact wires are to be inserted. For example, when inserting the wire I5 the tube is severed along the line to provide upper and lower sections I8 and I9 as shown in Fig. 2 and the wire is arranged in a position at one side of the base so as to form a chord in the inner wall of the bore I2, as indicated in Figs. 2 and 3. A portion of the wall of the bore, for example the portion 24, lying at one side of the transverse center of the wire is turned outwardly into contact with the curved lateral surface of the wire, whereby a relatively large area II or" the wire is exposed for contact with the mercury column.

While the invention is illustrated herein in connection with one specific form of thermostat it is to be understood that the form of thermostat herein shown is merely for the purpose of illustration and is not intended as a limitation. The thermostat is also described herein as Yincluding a mercury column I6, but it is intended that the invention shall extend to all thermostats of this general type regardless of whether the column is mercury or other liquids or amalgains.

We claim:

n 1. A thermostat of the liquid column type comprising a glass tubular body formed with a small 4 central bore for housing a liquid column of electro-conductive material, and a metallic electrical conductor in the form of a smooth cylindrical wire embedded in the wall of the tube and extending entirely across thetube on a line which intersects the circumference of the central bore at one side thereof, whereby a portion of the smooth transversely curved lateral surface of said conductor protrudes slightly into said bore for making electrical contact with said liquid column.

2. A thermostat of the liquid column type comprising a glass tubular body formed with a small central bore for housing a, liquid column of electro-conductive material, and a metallic electrical conductor in the form of a smooth cylindrical wire of small diameter embedded in the wall of the tube and extending entirely across the tube at one side of the central bore in close arrangement to the edge thereof and having a portion of its smooth transversely curved lateral surface protruding slightly into said bore for making electrical contact with said liquid column, either end of the said wire providing a ow path for electrical current.

3. A thermostat of the liquid column type comprising a glass tubular body formed with a small central bore for housing a liquid column of electro-conductive material, a metallic electrical conductor in the form o a smooth cylindrical wire or small diameter embedded in the wall of the tube and extending entirely across the tube with opposite ends protruding from the tube and having an intermediate portion of its smooth transversely curved lateral surface protruding slightly into the central bore at one side thereof for making electrical contact with said liquid column and whereby either end of the said wire serves as a ilow path for electrical current, and a metallic ring extending around the tube and engaging both ends of the said wire.

4. A thermostat of the liquid column type comprising a glass tubular body formed with a small central bore for housing a liquid column of electro-conductive material, and a metallic electrical conductor in the form of a wire having a smooth lateral surface embedded in the wall of the tube and extending entirely across the tube and communicating with the central bore thereof, a portion ofthe wall of said bore adjacent the wire and lying at oneside of its transverse center being turned outwardly into contact with the curved lateral surface of the wire,`whereby a substantial `area of vsaid smooth lateral suriacvzen of the metallic conductor` communicates with said bore for making electrical contact with said liquid column. N d u WILLIAM M.

BENJAMIN l?. FREBERG.

ALVA W. THARP.

REFERENCES CITED The following references are of record in the iile of this patent:

l U'Nirnn STATES PATENTS Number 

